With the expiration of the federal assault weapons ban, most Americans are able to legally perform this procedure. While it WAS a prohibited procedure under the 1994 assault weapons ban which regulated "large capacity magazines" over 10 rounds, it is no longer federally prohibited. However, certain STATES do have magazine capacity legislation, and GunWiki strongly discourages people from performing this procedure where it is prohibited by law to possess or manufacture high capacity magazines. By the BATF's most stringent interpretation, modifying a magazine to hold a different caliber or to fit into a different gun does constitute the manufacture of a "new" high capacity magazine out of the parts of the "old" high-capacity magazine. However, the BATF no longer cares about this, as the federal law has expired.

Now, the legitimate interest in this procedure is pretty clear. With the expiration of the assault weapons ban, folks are free to have full capacity 40cal magazines. I believe in the CZ-75 they go up to 12 or so. That leaves a fair number of 10-round 40cal magazines lying around unused. Since they can be converted to full-capacity 15 ronud 9mm magazines, they don't have to sit on the shelf.

This procedure will also work with magazines for the Magnum Research "Baby Eagle" pistol, as the pistols themselves are just modified CZ-75 clones.

And now, for the procedure.

The CZ-75B frame and magazine well are the same between the 40cal and 9mm versions. The only difference in the magazines is that the feed lips are a bit narrower in the 9mm version. Due to the larger size of the 40cal round, a 10rd 40cal magazine does not have a spacer at the bottom to prevent more than 10 rounds from being loaded into it. Therefore, the only modification required to convert a 10-round 40cal magazine into a full-capacity 9mm magazine is the bending of the feed lips.

This procedure requires a few 9mm rounds (live or inert) and a pair of pliers. I would recommend also having some 40cal rounds around (live or inert).

I recommend a using a pair of pliers with electrical tape or other material on the metal jaws, in order to prevent the finish on the magazine from being scratched up. It only takes a few millimeters of bend on the feed lips. I would recommend bending it a little bit, then putting a 9mm round into the magazine and seeing if it fits. Once one round fits, load as many as the magazine will hold. I believe that 15 rounds is normal for a magazine which has been modified in this way. If the top round pops out of the magazine, you need to move the lips inwards just a little bit more. I would also recommend shaking the magazine around vertically a little, just to make sure that you've got the spacing correct and that rounds do not pop out the top.

The interesting thing is that if you've been conservative enough in your modifications, the magazine will now feed both 40cal and 9mm rounds. Careful when you're shooting, and make sure you don't chamber the wrong one! Of course, if you're firing both a 9mm and 40cal CZ-75, then you already have had to worry about that due to having magazines that would fit into the other weapon anyway.

At any rate, once you've verified that the rounds will not jump out of their own accord, your next step is to test-fire your weapon with the new magazine at a shooting range. I would recommend bringing along your pliers, just in case you find that it's not feeding properly. If you've unevenly bent the feed lips or bent them too far, you may have feed issues. Once your magazine has been filled to capacity and then emptied a few times, feeding reliably, you should feel confident in using your new full-capacity 9mm magazine.

Do not rely on this newly-modified magazine for anything critical (self defense, concealed carry, etc) until you have used it at a range several times and verified that it feeds properly!

PS - For anyone presently living in a free state, I have a homework assignment: Find out just how many 40cal rounds one of the new CZ-75 17rd magazines can hold if you bend open the feed lips a little!